The present invention relates to a concrete breaker used for demolishing buildings.
As means for breaking iron-reinforced concrete buildings, bridges and the like, and as means for crushing concrete blocks of a demolished concrete building into pieces, use has been made of an open-close jaw type concrete breaker. Such concrete breaker breaks concrete blocks by a pair of upper and lower jaws of steel which open and close. A conventional concrete breaker of this type will now be described with reference to FIGS. 9 and 10.
A concrete breaker shown in FIG. 9 is the one disclosed in Japanese Utility Model Publication [Kokoku] No. 28839/1986 and Japanese Utility Model Application Disclosure [Kokai] No. 177258/1985, and comprises a swing arm 3 rotatably connected to the front end of a boom 2 tiltably extending from a working machine 1 and a lower jaw 61 and an upper jaw 62 openably and closably connected to the front end of said swing arm 3. The boom 2 is vertically swung by a hydraulic cylinder 15, while the swing arm 3 is driven back and forth by a hydraulic cylinder 16 attached to the boom 2.
The lower jaw 61 is rotatably connected at its rear end to the front end of the swing arm 3 by a pin 70. The rear end of the lower jaw 61 is connected through a link mechanism 72 to the front end of the piston rod 71 of a hydraulic cylinder 17 attached to the swing arm 3. The lower jaw 61 is turned back and forth by the hydraulic cylinder 17. The rear end of the upper jaw 62 is rotatably connected to the middle portion of the lower jaw 61 by a pin 63. The upper jaw 62 is pivotally moved (for opening and closing) with the pin 63 serving as a fulcrum at the position where it is opposed to the front end of the lower jaw 61. The opening and closing movement of the upper jaw 62 is performed by a hydraulic cylinder 64 attached between the lower and upper jaws 61 and 62.
As shown in FIG. 10, the lower jaw 61 has lower cutting blades 65 in the form of a lattice at the front end and the upper jaw has a plurality of projection-like upper cutting blades 66. As shown in FIG. 10(a), with the upper jaw 62 opened, a concrete block 18 is pushed into the space between the lower and upper jaws 61 and 62 and the upper jaw 62 is closed toward the front end of the lower jaw 61 by the hydraulic cylinder 64, whereby the concrete block 18 is broken by the lower and upper cutting blades 65 and 66, as shown in FIG. 10(b). Most of the broken pieces 18' from the concrete block 18 fall through openings 67 defined by the lattice-like lower cutting blades 65 of the lower jaw 61. The broken pieces 18' are further broken for various uses.
The concrete breaker of the opening and closing type described above has the following problems.
Since broken pieces 18' have to be allowed to fall through the openings 67, if the size of the openings 67 is decreased to that of ballast, then clogging tends to occur. If the size of said openings is set at a value well above the size of ballast, then the broken pieces 18' fall through the openings 67 before they are finely broken, with the result that the average size of the broken pieces 18' becomes greater than that of ballast. Therefore, if the broken pieces 18' are to be used as ballast, they have to be broken by separate concrete breaking means, this operation being troublesome.
Since the front end of the lower jaw 61 is the region where the openings 67 are formed and hence it has a lower mechanical strength, thick steel material has to be used for the lattice-like lower cutting blades 65 themselves and their support means and reinforcing means. As a result, the lower jaw increases in size, becoming heavier.
The piston rod 68 of the hydraulic cylinder 64 for opening and closing the upper jaw 62 with respect to the lower jaw 61 is exposed and hence is liable to be damaged or contaminated as it hits against a concrete wall at the work site during concrete breaking operation. To prevent such a drawback, a protective cover (not shown) which entirely covers the hydraulic cylinder 64 is fixed on the lower jaw 61, as is practiced in some concrete breakers of the opening and closing jaw type. However, the installation of such protective cover increases the size of the entire jaw and interferes with concrete breaking operation, making it impossible to perform concrete breaking operation in narrow spaces.